November 27 – Atmosphere on an Extrasolar Planet!

Posted
on November 27, 2015

Have
you ever heard of an extraterrestrial (E.T.) creature?

An
extraterrestrial creature would be an creature that is “not of the
Earth,” because one name for our planet is Terra. (The word terra,
lower case, means land or territory. And of course earth,
lower case, means soil or dirt. We tend to double-dip our words for
our planet!)

What
about extrasolar? What does that mean?

A
creature who is extrasolar is “not of our solar system.” We often
call our local star the Sun, but sometimes we call it Sol. Another
star system would have its own star or stars, and perhaps some
planets, satellites, asteroids, dwarf planets, and comets.

For
as long as there have been humans, we have wondered if there were
other worlds. Part of the excitement of astronomy has been to confirm
that some of the lights in the sky are, indeed, entirely separate
worlds (the Moon, Venus, Jupiter's moon Io, and so forth). Very
encouraging, if we care about finding other forms of life.

But
part of astronomy has been to discover the enormous, enormous
distances in space. Huge gaps between worlds in our solar system, and
even huger – GIGANTIC - gaps between stars and tremendously huger
and amazingly gigantic gaps between galaxies.

Those
huge distances means that our chances of discovering other lifeforms
plummet from what we first imagined... Still, thanks to the
cleverness of astronomers, we have been able to do what seemed almost
impossible in my childhood:

Even
though they are so amazingly far away, we have been able to discover
extrasolar planets – planets circling other stars. Starting in
1992, scientists have used red- and blue-shifted light, light dimmed
from transits, gravitational microlensing, and super-precise
measurements of stars' positions to detect planets circling other
stars. We have even been able to directly image a few planets!

At
this point, just a bit more than two decades into the exoplanet biz,
we have already discovered thousands!

As
you have probably already guessed, we are especially interested in
discovering extrasolar planets that are Earthlike – planets that
are located in the Goldilocks Zone of their suns (you know, not too
cold and not too hot), and planets that are in Goldilocks-ish
size-wise, too (not too large and not too small). Unfortunately, with
the methods we have at our disposal, it's much easier to detect
enormous gas giants that are far from their stars (not very friendly
to life as we know it) than it is to detect smaller rocky planets
that are warm enough for liquid water and, we hope, life.

On
this date in 2001, scientists discovered the first atmosphere on an
exoplanet. Utilizing data from the Hubble Space Telescope, they
determined that that the exoplanet often called Osiris has an
evaporating hydrogen atmosphere with some oxygen and carbon.

Osiris's
official name is HD 209458 b. But that official name is hard to
remember and not very colorful. So we are going to stick with the
unofficial “Osiris”!

Osiris's
sun is HD 209458 – that star needs a cool name! If it were visible
to the naked eye from us Earthlings, Osiris and its sun would be seen
in the constellation Pegasus. The star system is about 150 light
years from our solar system.

(That
means that it takes light 150 years to travel from Osiris's sun to us
here on Earth.)

By
the way, Osiris is “the first” in several other categories, aside
from the “detectable atmosphere” category. It was the first
exoplanet detected transiting its star, the first exoplanet detected
through multiple methods, and the first to have its orbital speed
measured.

By
the way, I mentioned that it is easier to directly detect a planet
that is far away from its star, but Osiris is really, really close to
its star. It whips around its sun in a much closer orbit than
Mercury's orbit around the Sun, so its year is just 3 and a
half Earth days long! Being so to a star, the planet is pretty
hot—about 1,800 degrees F (1,000 degrees C)!

Osiris
is also enormous – it would have to be, to hold onto a hydrogen
atmosphere! It's larger than Jupiter:

Osiris (right) is larger than the largestplanet in our solar system, Jupiter (left).

Since hydrogen is the lightest element in the universe, it doesn't take much to blow it off a planet. The heat and stellar wind coming off Osiris's sun are literally boiling away its atmosphere and, scientists have guessed, the escaping gas forms a tail rather like a comet's tail. It will take a trillion years for the entire planet to evaporate.

Here's an artist rendition of what Osiris's tail might look like, as seen from a rocky planet or moon:

And here is another artist's rendition of "the evaporating planet":

You can see that Osiris is not a Goldilocks planet. It's too big AND too hot, and we don't expect that life-as-we-know-it could exist there. (Although it's anyone's guess when we consider life as we DON'T know it!)

Our solar system doesn't have any gas giants close to the Sun, but we have discovered several so-called “hot Jupiters” in other star systems. Some other terms for gas giants that circle their star in
very close orbit, aside from “hot Jupiters,” include roaster
planets, epistellar jovians, pegasids, and pegasean planets.

About Me

This site is designed to be a source of interesting articles for kids and a resource for teachers and parents (especially homeschool teacher/parents!). From world holidays to historical anniversaries, Every Day Is Special celebrates each and every day.